The present disclosure relates to a temperature adaptive radial shaft sealing device that provides improved sealing over a wide range of temperatures while minimizing the friction and wear associated with the same.
Most automotive sub-systems such as the engine, transmission, driveline, suspension dampers, pumps, brakes and other hydraulic/pneumatic actuators utilize seals to prevent ingress of extraneous materials (dust, dirt, humidity, air etc.) into the actuators and/or egress of fluids from the actuators. The seals can be used in a static or a dynamic application. Most dynamic seals have at least one part of the seal in contact with a sliding or a rotating surface. As an example, a shock absorber has a cylindrical piston rod that reciprocates axially through a sealed bearing embedded at one end of a closed cylindrical tube that encloses a hydraulic fluid. As another example, most rotating elements in the transmission require the use of rotary dynamic seals to prevent leakage of the pressurized hydraulic fluid, e.g., prevent leaking past the shaft bearings.
Many types of radial shaft seals suitable for individual applications are available commercially. Each seal application has specific requirements in terms of the leakage rate, operating temperature range, maximum allowable friction, misalignment, cost, cycle life, and the like. In automotive applications, the ambient temperatures in which the seals must effectively operate typically range from about −40° C. to about 150° C. while the temperatures that some of the seals experience may be over an even wider temperature range, such as −55° C. to 250° C. or more. While commercially available radial shaft seals satisfy most of the requirements of a given application at one temperature extreme, it is difficult to satisfy all of the requirements at both temperature extremes. For example, it is oftentimes difficult to minimize seal friction at temperatures at the lower end of the extremes (freezing and below) while maintaining adequate seal friction/minimum leakage at the temperatures approaching the higher end of the temperature extremes (temperatures in excess of 100° C.). Most prior art seals utilize spring loaded elastomer materials to maintain adequate sealing over time and temperature. However, because of thermal expansion properties inherent to the materials (e.g., spring steel, aluminum, brass, and the like) used to form the spring, uniform spring loads do not occur over the wide temperature ranges to which seals are exposed such as experienced by dynamic seals used in the automotive environment.
The disadvantages of prior art radial shaft seals include, but are not limited to, excessive friction, excessive leakage, excessive wear, reduced life/durability, and non-uniform compliance/sealing pressure over the required operating temperature range, among others. Interestingly, the first two properties are at odds with each other in a dynamic sealing situation. Good compression forces holding the seal against a reciprocating or rotating member accelerate seal wear and shorten service life whereas reducing the compressive force can result in leaking, especially at the temperature extremes in which the dynamic seal device can be used. Therefore, every dynamic seal design is a compromise to produce an acceptable balance between these two desirable properties.
Accordingly, what is needed is an improved seal assembly that operates effectively and uniformly across a wide temperature range.